TSH

This large prospective cohort study investigated the relationship between early pregnancy thyroid function and the risk of gestational diabetes mellitus (GDM), utilizing data from 26,742 pregnant women recruited through the China Birth Cohort Study (CBCS). Among these, 3,985 women (14.90%) were diagnosed with GDM. Women with GDM were generally older than those without GDM (33.26 ± 4.01 vs. 31.51 ± 3.76 years, P < .001). After adjusting for potential confounders, elevated thyroid-stimulating hormone (TSH) levels (aOR 1.030, 95% CI 1.007–1.054, P = .012) and subclinical hypothyroidism (aOR 1.211, 95% CI 1.010–1.451, P = .039) were positively associated with GDM risk. However, free thyroxine and thyroid peroxidase antibody were not significantly linked to GDM. A nonlinear relationship between TSH and GDM was observed: when TSH ≤ 1.24 mIU/L, GDM risk increased with higher TSH levels, but this trend plateaued when TSH exceeded 1.24 mIU/L. These findings highlight the role of thyroid dysfunction, particularly elevated TSH, in the development of GDM and suggest the need for early thyroid function screening during pregnancy.